The present invention relates generally to semiconductor fabrication, and more particularly to methods for fabricating improved ultra-large scale integration (ULSI) semiconductor devices including ULSI metal oxide silicon field effect transistors (MOSFETs).
Semiconductor chips or wafers are used in many applications, including use as processor chips for computers, use as integrated circuits, and use as flash memory for hand-held computing devices, wireless telephones, and digital cameras. Regardless of the application, a semiconductor chip desirably holds as many circuits or memory cells as possible per unit area. In this way, the size, weight, and energy consumption of devices using semiconductor chips advantageously is minimized, while, nevertheless, improving the memory capacity and computing power of the devices.
A common circuit component of semiconductor chips is the transistor. In ULSI semiconductor chips, a transistor is established by forming a polysilicon gate on a silicon substrate, and then forming a source region and a drain region side by side in the substrate beneath the gate by implanting appropriate dopant materials into the areas of the substrate that are to become the source and drain regions. The gate is insulated from the source and drain regions by a thin gate oxide layer, with small portions of the source and drain regions, referred to as xe2x80x9cextensions,xe2x80x9d extending toward and virtually under the gate. This generally-described structure cooperates to function as a transistor.
MOSFETs having so-called xe2x80x9craisedxe2x80x9d source and drain regions have been provided, in which the source and drain regions extend above the surface of the substrate alongside the gate stack. Such structures advantageously exhibit less source/drain junction series resistance and provide more room for silicidation than conventional MOSFET structures, thereby improving transistor performance.
Epitaxy has been used to form the raised source/drain structure. As recognized herein, the epitaxial process entails the use of relatively high temperatures. The amount of heat used to make semiconductors is colloquially referred to as the xe2x80x9cthermal budgetxe2x80x9d of a process. Minimizing the thermal budget is important,because a high thermal budget can cause unwanted side effects, such as dopant diffusion into well regions and into channel implant regions and warping of the chip. With the foregoing background in mind, the present invention recognizes the desirability of minimizing the thermal budget in a raised source/drain semiconductor chip fabrication process.
A method is disclosed for establishing one or more raised source/drain regions on a semiconductor substrate. The method includes forming at least one gate stack on the substrate, and then disposing an amorphous silicon film over the substrate and gate stack. The film is polished down to the top surface of the gate stack and further is etched away after polishing. Dopant is then implanted into the film, and the film is irradiated with an excimer laser melt at least portions of the film and crystallize the silicon. After irradiating, annealing is undertaken to silicidize the film and activate the dopant in the film to thereby establish raised source/drain regions.
In another aspect, a method for establishing one or more raised source/drain regions on a semiconductor substrate includes disposing an amorphous silicon film on the substrate, and irradiating the film with laser light to melt at least portions of the film.
Other features of the present invention are disclosed or apparent in the section entitled xe2x80x9cDETAILED DESCRIPTION OF THE INVENTION.xe2x80x9d